Evolution of life history traits
Jean-François Le Galliard
CNRS, UMR 7625, Ecologie-Evolution CNRS, UMS 3194, CEREEP – Ecotron Ile de France
Course program
Section 1 – A quick guide to life history evolution
Section 2 – Life history variation in reptiles
Section 3 – Observed reproductive strategies in the meadow viper
Section 4 – Evolution of reproductive effort and breeding frequencies
in the meadow viper
Section 1 – A quick guide to life history evolution
Section 1 – Life history evolution
Life history evolution: A general framework based on quantitative genetics, population ecology and physiology to understand variation and adaptation in life history strategies.
Life history strategies (demographic tactics): Ensemble of life history traits of a given individual, population, species or higher taxa.
Life history traits: Traits that are directly involved into a characteristic equation describing individual fitness; such age at maturity, survival and reproduction (Roff 2002). Life history traits are coupled into a life cycle and their interactions determine individual fitness, population growth or the species growth/competitive ability.
Standard life history traits
Pre-maturation traits Body growth early in life Juvenile and sub-adult survival Age and size at sexual maturation Natal dispersal Post-maturation traits Body growth during adult life Reproductive effort (number and quality of offspring) Adult survival Breeding dispersal Post-reproductive traits Length of post-reproductive life span Aging http://images.google.fr
A scheme for life history evolution
External conditions ?
Phenotypic variation and covariation / local conditions ? LHS(parent,i) = {LH1(i),LH2(i), …}
Parental generation
Differential reproduction and inheritance ? LHS(t) = {E(LH1),E(LH2), …}
LHS(offsprings,i) = {LH1(i),LH2(i), …} Differential survival ? Phenotypic and evolutionary changes ?
External conditions ?
Parental generation
LHS(t) = {E(LH1),E(LH2), …}
Basic concepts in life history evolution
Variation, inheritance and response to selection Most traits vary but only part of the variation is “inherited” from one generation to another Response to selection (S) is given by the breeder equation:
Fitness surfaces, multivariate selection and genetic variances Fitness surfaces can be used to describe natural and sexual selection on traits Linear models can be used to assess the strength of selection on traits: s Response to selection then depends on variance and covariance of traits
Example of trait variation & fitness surfaces
Le Galliard et al. Nature 2004
Another example of fitness surfaces
http://images.google.fr
Preziosi & Fairbairn. Evolution 1997.
Correlational selection & fitness surfaces
Sinervo & Svensson. Heredity 2002.
Basic concepts in life history evolution
Life-history trade-offs & external conditions act as the main driver of life history evolution Trade-offs result from allocation rules of limited energy and competing demands of organismal functions, such as maintenance, growth or reproduction. They result in negative phenotypic correlation between traits and can be expressed as negative genetic correlations as well (e.g. costs of reproduction). Ecological and social conditions (e.g. background mortality at the adult stage) influence the costs and benefits of alternative life history strategies
Ecological and social conditions vary substantially in time and space Spatial variation is important to understand the evolution of dispersal and local adaptation (see dispersal evolution) Temporal variation is important for the evolution of phenotypic plasticity and bet-hedging (variance reduction strategy)
Illustration of a phenotypic trade-off
http://godofinsects.com/
Roff et al. Evolution 2002
Adaptive radiation and life history evolution
Rivulus communities Low predation
http://images.google.fr
Low reproductive effort Long brood intervals and delayed maturity Large embryos and smaller litters
Crenicichla communities High adult predation High reproductive effort Short brood intervals and early maturity Small embryos and large litters http://images.google.fr
Schluter. TREE. 2001
Reznick. Evolution 1982
Section 2 – Life history variation in reptiles
Phylogeny of squamata reptiles TREE of LIFE web project Conrad. 2008
Zardoya & Meyer. PNAS. 1998
Squamata reptiles (lizards, snakes and amphisbenians) Diapsid amniotes close to « lizards » type Distributed throughout the world with diverse taxa in tropics and desertic/semi-desertic habitats Several thousands of species on earth
Reproductive strategies in squamate reptiles http://images.google.fr
Frequent breeding, iteroparous Flexible clutch size and reproductive effort Short life, early age at sexual maturity Small body size
Income breeding Active foraging strategies Uta stransburiana Egg-laying species, high adult and juvenile mortality Multiple clutches per year (2-3) Variable litter sizes and offspring size Active foragers Small adult body size (< 4g) but relatively large sizeindependent reproductive effort
Infrequent breeding, semelparous Constant clutch size and reproductive effort Long life, late sexual maturation Large body size
Capital breeding Sit-and-wait foraging strategies Eunectes murinus Viviparous species, high adult survival One litter per year or every other year Ambush predators Large adult body size (
